Observations of T Tauri Disks at Sub-AU Radii: Implications for Magnetospheric Accretion and Planet Formation

We determine inner disk sizes and temperatures for four solar-type (1-2 M$_{\odot}$) classical T Tauri stars (AS 207A, V2508 Oph, AS 205A, and PX Vul) using 2.2 $\mu$m observations from the Keck Interferometer. Nearly contemporaneous near-IR adaptive optics imaging photometry, optical photometry, and high-dispersion optical spectroscopy are used to distinguish contributions from the inner disks and central stars in the interferometric observations. In addition, the spectroscopic and photometric data provide estimates of stellar properties, mass accretion rates, and disk co-rotation radii. We model our interferometric and photometric data in the context of geometrically flat accretion disk models with inner holes, and flared disks with puffed-up inner walls. Models incorporating puffed-up inner disk walls generally provide better fits to the data, similar to previous results for higher-mass Herbig Ae stars. Our measured inner disk sizes are larger than disk truncation radii predicted by magnetospheric accretion models, with larger discrepancies for sources with higher mass accretion rates. We suggest that our measured sizes correspond to dust sublimation radii, and that optically-thin gaseous material may extend further inward to the magnetospheric truncation radii. Finally, our inner disk measurements constrain the location of terrestrial planet formation as well as potential mechanisms for halting giant planet migration.Comment: Accepted for publication in ApJ (May 1, 2005 issue

Nonlinear acoustic waves in channels with variable cross sections

The point symmetry group is studied for the generalized Webster-type equation describing non-linear acoustic waves in lossy channels with variable cross sections. It is shown that, for certain types of cross section profiles, the admitted symmetry group is extended and the invariant solutions corresponding to these profiles are obtained. Approximate analytic solutions to the generalized Webster equation are derived for channels with smoothly varying cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic corrections introduced mainly in the Introduction and References. Several typos were also correcte

Two Late Quaternary Pollen Records from South-Central Alaska

Pollen records from Wonder and Ten Mile lakes, located at aititudinal treeline to the north and south of the Alaska Range respectively, document the vegetation history of a portion of the southern Alaskan boreal forest. The new pollen diagrams indicate a Betula shrub tundra, preceded at Wonder Lake by a sparse herb tundra, which characterized these two areas during latest Wisconsinan times. Populus was in the vicinity of Ten Mile Lake ca. 10,000 BP, but was apparently absent from Wonder Lake. Picea glauca grew at or near Ten Mile Lake by 9100 BP, with P. mariana becoming important ca. 7000 BP. The first forests at Wonder Lake were also dominated by P. glauca and followed by increased numbers of P. mariana. The timing of forest establishment at Wonder Lake is uncertain due to problematic radiocarbon dates. Alnus appears to be common in both regions by ca. 7000 BP. These records suggest that paleo-vegetational reconstructions are more difficult for the southern than northern boreal forests in Alaska because of greater topographic diversity, difficulties with over-representation of some pollen taxa, and problems with radiocarbon dating. Despite these concerns, available data from south-central Alaska suggest that southern and northern forests differ in their vegetational histories. Such differences, when related to temperature fluctuations that have been postulated for the Holocene, imply that the Alaskan boreal forest may not respond uniformly to future global warming.Les inventaires polliniques de Wonder Lake et de Ten Mile Lake, situés à la limite altitudinale des arbres au nord et au sud de la chaîne de l'Alaska permettent de reconstituer l'histoire de la végétation d'une portion de la forêt boréale du sud de l'Alaska. Les nouveaux diagrammes polliniques montrent une toundra arbustive à Betula, précédée au Wonder Lake par une toundra herbacée clairsemée, à la fin du Wisconsinien. Vers 10 000 BP, Populus était dans les environs du Ten Mile Lake, mais était apparamment absent du Wonder Lake. Picea glauca croissait autour du Ten Mile Lake à 9100 BP et P. mariana prenait de l'importance vers 7000 BP. Au Wonder Lake, les premières forêts ont également été dominées par P. glauca, puis par un nombre croissant de P. mariana. La chronologie de !'afforestation est incertaine en raison de datations au radiocarbone douteuses. Alnus semble être une espèce courante dans les deux régions vers 7000 BP. Les inventaires indiquent que la reconstitution de la paléovégétation est plus difficile à faire pour les forêts méridionales que septentrionales de l'Alaska, en raison de la plus grande diversité topographique, la sur-représentation de certains taxons et des problèmes de radio-datation. Les données indiquent tout de même que l'histoire de la végétation des forêts diffèrent au nord et au sud. Ces différences, mises en relation avec les fluctuations de températures présumées de l'Holocène, laissent croire que la forêt de l'Alaska ne répondra pas nécessairement de façon uniforme à un réchauffement climatique éventuel.DbiJibneBbie aiiarpa.viMbi ocaaKOB 03ep Baeae n TeHMaRJi, pacnojioxeHiibix B6JIII3H Bepxiiert rpaiiMUbi Jieca Ha ceBepe H wre A/iflCKiiHCKoro xpeôîa, OTpaacaioT ncropnio pacTHTejibHOCTH KOKIIOH lacr" Sopea/ibHoro jieca AJIBCKH. HoBbie ribiJibuebe anarpaMMbi iiOKaabiBaioT, HTO KycTapmiKOBOfi 6epr30B0fi TyHApe, xapaKTepiioft aJifl 3TMX aByx TeppiiTopufl B Teieime no3iuiero BiicKoiicmia, npemuecTBOBajia B oTaoaceiinnx 03. Banae 6emiaH TpaBHHUCTHa iyHapa. Populus iipopn3parra.n B otcpecruocnix 03. Teii.vianji 10000 /J.H., HO, JlO-BIUHMOMy, OTCyTCTBOBaa B pafione 03. BaHae. 9100 JI.H. B panoHe 03. Tenvianj] H.11I B iienocpeacrBeimoH 6/IH30CTH OT iiero npoH3pacTajia Picea glauca, KOTopan BMepTe c Picea mariana nrpaeT 3Ha'iiiTe/ibnyio pojib B codaBe pacTHTeJibHOCTM OKO/IO 7000 .i.n. B nepBbix Jiecax B paflone 03. BaHae TaKjKe aoMiiiuipoBajia Picea glauca, 110 3aTe,vi pojib Picea mariana iiaHimaeT B03pacacTaTb. Bpe.viH noflB/ieiiHfl jiecoB B panone 03. Banae uoKaiie ycraiiaBJiiiBaeTca iiaaeacHo paaiioyr-jiepoaiibiM McroaoM. Alnus o6pa3yer cooBiuecTBa B06011X pafioiiax OKOJIO 7000 JI.H. nojiyieiuibie aaiiHbie cBiiaeTejibCTByioT 0 TOM, HTO peKoiicTpyKniifl pacTiiTejibiiocTH 6yaer 6ojieecjio>KHon aJin lOîKHbix, ieM aJifl ceaepiibix 6opeajibiibix JiecoB AJIHCKH 1133a SHa'iinejibiioro TonorpafpimecKoro iiecxoacTBa,3aTpyaiieiii!Ji B iiHTepnpeTaumi neKOTopwx nbijibneitbix TaKCOHOB, npoGjieM c paanoyrjiepoaiibiM aaTHpBaiine.M. HeavioTpa tia 3TH npo6jieivibi, nojicpieHHbie aaHiibie noKa3biaiOT, HTO fjopeajibiibie Jieca 11a wre 11 ceBepe ioaciion iacni UetiTajibiion AJIHCKH wweioT pa3Jiiiiyio iiCTopnio. TaKiie pa3Jinmtfl, cBfl3xaiuibie c n3MeiieiijiflMii 3eMJiepaTyp B Teieiuie ro.'ioueiia, cBiiae-Te.TbCTByioT, HTO 6opeajibiibiri Jiec AJIHCKH ,vioxer ne OTBenaTb cienapnio rjio6aJibiioro noTen.ieiina u SyaymeM

Accreting Protoplanets in the LkCa 15 Transition Disk

Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1900 exoplanets have now been discovered and confirmed, none are still in the process of formation. Transition discs, protoplanetary disks with inner clearings best explained by the influence of accreting planets, are natural laboratories for the study of planet formation. Some transition discs show evidence for the presence of young planets in the form of disc asymmetries or infrared sources detected within their clearings, as in the case of LkCa 15. Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful. Here we report adaptive optics observations of LkCa 15 that probe within the disc clearing. With accurate source positions over multiple epochs spanning 2009 - 2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect H{\alpha} emission from the innermost companion, LkCa 15 b, evincing hot (~10,000 K) gas falling deep into the potential well of an accreting protoplanet.Comment: 35 pages, 3 figures, 1 table, 9 extended data item

ASTRA: ASTrometry and phase-Referencing Astronomy on the Keck interferometer

ASTRA (ASTrometric and phase-Referencing Astronomy) is an upgrade to the existing Keck Interferometer which aims at providing new self-phase referencing (high spectral resolution observation of YSOs), dual-field phase referencing (sensitive AGN observations), and astrometric (known exoplanetary systems characterization and galactic center general relativity in strong field regime) capabilities. With the first high spectral resolution mode now offered to the community, this contribution focuses on the progress of the dual field and astrometric modes.Comment: 10 pages, 6 figures, 2 tables, SPIE 201

Evidence for Neutrino Oscillations from Muon Decay at Rest

A search for nu_bar_mu to nu_bar_e oscillations has been conducted at the Los Alamos Meson Physics Facility using nu_bar_mu from mu+ decay at rest. The nu_bar_e are detected via the reaction (nu_bar_e,p) -> (e+,n), correlated with the 2.2 MeV gamma from (n,p) -> (d,gamma). The use of tight cuts to identify e+ events with correlated gamma rays yields 22 events with e+ energy between 36 and 60 MeV and only 4.6 (+/- 0.6) background events. The probability that this excess is due entirely to a statistical fluctuation is 4.1E-08. A chi^2 fit to the entire e+ sample results in a total excess of 51.8 (+18.7) (-16.9) (+/- 8.0) events with e+ energy between 20 and 60 MeV. If attributed to nu_bar_mu -> nu_bar_e oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of 0.0031 (+0.0011) (-0.0010) (+/- 0.0005).Comment: 57 pages, 34 figures, revtex, additional information available at http://nu1.lampf.lanl.gov/~lsnd

Gene Function Classification Using Bayesian Models with Hierarchy-Based Priors

We investigate the application of hierarchical classification schemes to the annotation of gene function based on several characteristics of protein sequences including phylogenic descriptors, sequence based attributes, and predicted secondary structure. We discuss three Bayesian models and compare their performance in terms of predictive accuracy. These models are the ordinary multinomial logit (MNL) model, a hierarchical model based on a set of nested MNL models, and a MNL model with a prior that introduces correlations between the parameters for classes that are nearby in the hierarchy. We also provide a new scheme for combining different sources of information. We use these models to predict the functional class of Open Reading Frames (ORFs) from the E. coli genome. The results from all three models show substantial improvement over previous methods, which were based on the C5 algorithm. The MNL model using a prior based on the hierarchy outperforms both the non-hierarchical MNL model and the nested MNL model. In contrast to previous attempts at combining these sources of information, our approach results in a higher accuracy rate when compared to models that use each data source alone. Together, these results show that gene function can be predicted with higher accuracy than previously achieved, using Bayesian models that incorporate suitable prior information

Inside-Out Evacuation of Transitional Protoplanetary Disks by the Magneto-Rotational Instability

How do T Tauri disks accrete? The magneto-rotational instability (MRI) supplies one means, but protoplanetary disk gas is typically too poorly ionized to be magnetically active. Here we show that the MRI can, in fact, explain observed accretion rates for the sub-class of T Tauri disks known as transitional systems. Transitional disks are swept clean of dust inside rim radii of ~10 AU. Stellar coronal X-rays ionize material in the disk rim, activating the MRI there. Gas flows from the rim to the star, at a rate limited by the depth to which X-rays ionize the rim wall. The wider the rim, the larger the surface area that the rim wall exposes to X-rays, and the greater the accretion rate. Interior to the rim, the MRI continues to transport gas; the MRI is sustained even at the disk midplane by super-keV X-rays that Compton scatter down from the disk surface. Accretion is therefore steady inside the rim. Blown out by radiation pressure, dust largely fails to accrete with gas. Contrary to what is usually assumed, ambipolar diffusion, not Ohmic dissipation, limits how much gas is MRI-active. We infer values for the transport parameter alpha on the order of 0.01 for GM Aur, TW Hyd, and DM Tau. Because the MRI can only afflict a finite radial column of gas at the rim, disk properties inside the rim are insensitive to those outside. Thus our picture provides one robust setting for planet-disk interaction: a protoplanet interior to the rim will interact with gas whose density, temperature, and transport properties are definite and decoupled from uncertain initial conditions. Our study also supplies half the answer to how disks dissipate: the inner disk drains from the inside out by the MRI, while the outer disk photoevaporates by stellar ultraviolet radiation.Comment: Accepted to Nature Physics June 7, 2007. The manuscript for publication is embargoed per Nature policy. This arxiv.org version contains more technical details and discussion, and is distributed with permission from the editors. 10 pages, 4 figure

Museum education, cultural sustainability, and English language teaching in Spain

The collaborative action research project presented analysed the potential of museum education to radically transform the way in which English was taught and learnt in three diverse elementary, middle, and high-school contexts in the province of València (Spain). Insights from museum education and New Literacy Studies were used to expand upon the pedagogical affordances of the material and multimodal dimensions of English language teaching, in order to generate more opportunities for student motivation and engagement by connecting with the learners' home and community cultures, identities, languages, and literacies. To assess the impact of the project, a variety of qualitative strategies were used (including classroom recordings, student interviews and questionnaires, and photographs). A model for culturally sustaining pedagogy was suggested, which school and museum educators may use to inform their practice